1. The Cardiovascular System: Blood Vessels19
P A R T B
The Cardiovascular System: Blood Vessels

2. Long-Term Autoregulation
Is evoked when short-term autoregulation cannot meet tissue nutrient requirements
May evolve over weeks or months to enrich local blood flow

3. Long-Term Autoregulation
Angiogenesis takes place:
As the number of vessels to a region increases
When existing vessels enlarge
When a heart vessel becomes partly occluded
Routinely in people in high altitudes, where oxygen content of the air is low

4. Blood Flow: Skeletal Muscles
Resting muscle blood flow is regulated by myogenic and general neural mechanisms in response to oxygen and carbon dioxide levels
When muscles become active, hyperemia is directly proportional to greater metabolic activity of the muscle (active or exercise hyperemia)
Arterioles in muscles have cholinergic, and alpha () and beta () adrenergic receptors
 and  adrenergic receptors bind to epinephrine

5. Blood Flow: Skeletal Muscle Regulation
Muscle blood flow can increase tenfold or more during physical activity as vasodilation occurs
Low levels of epinephrine bind to  receptors
Cholinergic receptors are occupied

6. Blood Flow: Skeletal Muscle Regulation
Intense exercise or sympathetic nervous system activation results in high levels of epinephrine
High levels of epinephrine bind to  receptors and cause vasoconstriction
This is a protective response to prevent muscle oxygen demands from exceeding cardiac pumping ability

7. Blood Flow: Brain
Blood flow to the brain is constant, as neurons are intolerant of ischemia
Metabolic controls – brain tissue is extremely sensitive to declines in pH, and increased carbon dioxide causes marked vasodilation
Myogenic controls protect the brain from damaging changes in blood pressure
Decreases in MAP cause cerebral vessels to dilate to ensure adequate perfusion
Increases in MAP cause cerebral vessels to constrict

8. The brain is vulnerable under extreme systemic pressure changes
Blood Flow: Brain
The brain can regulate its own blood flow in certain circumstances, such as ischemia caused by a tumor
The brain is vulnerable under extreme systemic pressure changes
MAP below 60mm Hg can cause syncope (fainting)
MAP above 160 can result in cerebral edema

9. Blood flow through the skin:
Blood Flow: Skin
Blood flow through the skin:
Supplies nutrients to cells in response to oxygen need
Helps maintain body temperature
Provides a blood reservoir

10. Blood flow to venous plexuses below the skin surface:
Blood Flow: Skin
Blood flow to venous plexuses below the skin surface:
Varies from 50 ml/min to 2500 ml/min, depending on body temperature
Is controlled by sympathetic nervous system reflexes initiated by temperature receptors and the central nervous system

11. Temperature Regulation
As temperature rises (e.g., heat exposure, fever, vigorous exercise):
Hypothalamic signals reduce vasomotor stimulation of the skin vessels
Heat radiates from the skin
Sweat also causes vasodilation via bradykinin in perspiration
Bradykinin stimulates the release of NO
As temperature decreases, blood is shunted to deeper, more vital organs

12. Blood flow in the pulmonary circulation is unusual in that:
Blood Flow: Lungs
Blood flow in the pulmonary circulation is unusual in that:
The pathway is short
Arteries/arterioles are more like veins/venules (thin-walled, with large lumens)
They have a much lower arterial pressure (24/8 mm Hg versus 120/80 mm Hg)

13. Blood Flow: Lungs
The autoregulatory mechanism is exactly opposite of that in most tissues
Low oxygen levels cause vasoconstriction; high levels promote vasodilation
This allows for proper oxygen loading in the lungs

14. Small vessel coronary circulation is influenced by:
Blood Flow: Heart
Small vessel coronary circulation is influenced by:
Aortic pressure
The pumping activity of the ventricles
During ventricular systole:
Coronary vessels compress
Myocardial blood flow ceases
Stored myoglobin supplies sufficient oxygen
During ventricular diastole, oxygen and nutrients are carried to the heart

15. During strenuous exercise:
Blood Flow: Heart
Under resting conditions, blood flow through the heart may be controlled by a myogenic mechanism
During strenuous exercise:
Coronary vessels dilate in response to local accumulation of carbon dioxide
Blood flow may increase three to four times
Blood flow remains constant despite wide variation in coronary perfusion pressure

16. Capillary Exchange of Respiratory Gases and Nutrients
Oxygen, carbon dioxide, nutrients, and metabolic wastes diffuse between the blood and interstitial fluid along concentration gradients
Oxygen and nutrients pass from the blood to tissues
Carbon dioxide and metabolic wastes pass from tissues to the blood
Water-soluble solutes pass through clefts and fenestrations
Lipid-soluble molecules diffuse directly through endothelial membranes

17. Capillary Exchange of Respiratory Gases and Nutrients
Figure

18. Capillary Exchange of Respiratory Gases and Nutrients
Figure

19. Capillary Exchange: Fluid Movements
Direction and amount of fluid flow depends upon the difference between:
Capillary hydrostatic pressure (HPc)
Capillary colloid osmotic pressure (OPc)
HPc – pressure of blood against the capillary walls:
Tends to force fluids through the capillary walls
Is greater at the arterial end of a bed than at the venule end
OPc– created by nondiffusible plasma proteins, which draw water toward themselves

20. Net Filtration Pressure (NFP)
NFP – all the forces acting on a capillary bed
NFP = (HPc – HPif) – (OPc – OPif)
At the arterial end of a bed, hydrostatic forces dominate (fluids flow out)

21. Net Filtration Pressure (NFP)
At the venous end of a bed, osmotic forces dominate (fluids flow in)
More fluids enter the tissue beds than return blood, and the excess fluid is returned to the blood via the lymphatic system
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Autoregulation and Capillary Dynamics, pages 3–37

22. Net Filtration Pressure (NFP)
Figure 19.16

23. Circulatory Shock
Circulatory shock – any condition in which blood vessels are inadequately filled and blood cannot circulate normally
Results in inadequate blood flow to meet tissue needs

24. Circulatory Shock Three types include:
Hypovolemic shock – results from large-scale blood loss
Vascular shock – poor circulation resulting from extreme vasodilation
Cardiogenic shock – the heart cannot sustain adequate circulation

25. Figure 19.17

26. The vascular system has two distinct circulations
Circulatory Pathways
The vascular system has two distinct circulations
Pulmonary circulation – short loop that runs from the heart to the lungs and back to the heart
Systemic circulation – routes blood through a long loop to all parts of the body and returns to the heart

27. Differences Between Arteries and Veins
Delivery
Blood pumped into single systemic artery – the aorta
Blood returns via superior and interior venae cavae and the coronary sinus
Location
Deep, and protected by tissue
Both deep and superficial
Pathways
Fair, clear, and defined
Convergent interconnections
Supply/drainage
Predictable supply
Dural sinuses and hepatic portal circulation

28. Developmental Aspects
The endothelial lining of blood vessels arises from mesodermal cells, which collect in blood islands
Blood islands form rudimentary vascular tubes through which the heart pumps blood by the fourth week of development
Fetal shunts (foramen ovale and ductus arteriosus) bypass nonfunctional lungs
The ductus venosus bypasses the liver
The umbilical vein and arteries circulate blood to and from the placenta

29. Developmental Aspects
Blood vessels are trouble-free during youth
Vessel formation occurs:
As needed to support body growth
For wound healing
To rebuild vessels lost during menstrual cycles
With aging, varicose veins, atherosclerosis, and increased blood pressure may arise

30. Pulmonary Circulation
Figure 19.18b

31. Systemic Circulation
Figure 19.19

32. (b)
Common carotid arteries
Subclavian artery
Aortic arch
Coronary artery
Thoracic aorta
Branches of celiac trunk:
Renal artery
Superficial palmar arch
Radial artery
Ulnar artery
Internal iliac artery
Deep palmar arch •
Left gastric artery
Splenic artery
Common hepatic artery
Internal carotid artery
Vertebral artery
Brachiocephalic trunk
Axillary artery
Brachial artery
Abdominal aorta
Superior mesenteric artery
Gonadal artery
Common iliac artery
External iliac artery
Digital arteries
Femoral artery
Popliteal artery
Inferior mesenteric
artery
Ascending aorta
External carotid artery
Anterior tibial artery
Posterior tibial artery
Arcuate artery
Figure 19.20b

33. Ophthalmic artery Superficial temporal artery Basilar artery
Maxillary artery
Occipital artery
Facial artery
Vertebral artery
Internal
carotid artery
Lingual artery
External
carotid artery
Superior thyroid
artery
Common
carotid artery
Larynx
Thyrocervical
trunk
Thyroid gland
(overlying trachea)
Costocervical
trunk
Clavicle (cut)
Subclavian
artery
Brachiocephalic
trunk
Axillary
artery
Internal thoracic
artery
(b)
Figure 19.21b

34. Arteries of the Brain Anterior Cerebral arterial circle
(circle of Willis)
Frontal lobe
• Anterior
communicating
artery
Optic chiasma
Middle
cerebral
artery
• Anterior
cerebral artery
Internal
carotid
artery
• Posterior
communicating
artery
Pituitary
gland
• Posterior
cerebral artery
Temporal
lobe
Basilar artery
Pons
Occipital
lobe
Vertebral artery
Cerebellum
Posterior
(c)
(d)
Figure 19.21c,d

35. Common carotid
arteries
Vertebral artery
Thyrocervical trunk
Right subclavian
artery
Costocervical trunk
Suprascapular artery
Left subclavian
artery
Thoracoacromial artery
Axillary artery
Left axillary
artery
Subscapular artery
Brachiocephalic
trunk
Posterior circumflex
humeral artery
Posterior
intercostal
arteries
Anterior circumflex
humeral artery
Brachial artery
Anterior
intercostal
artery
Deep artery
of arm
Internal
thoracic
artery
Common
interosseous
artery
Descending
aorta
Radial
artery
Lateral
thoracic
artery
Ulnar
artery
Deep palmar arch
Superficial palmar arch
Digitals
(b)
Figure 19.22b